A specification of 3GPP (3rd Generation Partnership Project), which is a project aiming to standardize a cellular communication technology, supports a cellular/WLAN (Wireless Local Area Network) radio interworking technology in Release 12 and later.
With such a technology, a user terminal performs, on the basis of assistance information provided from a cellular communication network (RAN assistance parameters), a network selection operation for selecting an appropriate network, from the cellular communication network and a WLAN communication network, through which to transmit and receive traffic of the user terminal. The assistance information is appropriately updated according to a state of the cellular communication network and the like.